International patent Application No. PCT/AU2011/001556, dated 1 Dec. 2011, now International patent Publication No. WO 2012/071616 A1, published 7 Jun. 2012, based on Provisional Patent Application No. 2010905289, lodged in Australia in the names of Optint Pty Limited and University of Sydney on 1 Dec. 2010, discloses an integrated process for the production of ammonium nitrate in which:    a) a gaseous oxidiser feed composed at least substantially of ammonia, steam and an oxidising gas is exposed to conditions whereby the ammonia is oxidised to produce a reaction mixture including nitrogen monoxide and water vapour,    b) the reaction mixture is cooled in a heat exchanger whereby the nitrogen monoxide is oxidised, the water vapour is condensed and the products of the nitrogen monoxide oxidation react with and are absorbed by the condensed water to form a nitric acid stream, and    c) the nitric acid stream is reacted with a stream of ammonia to form the ammonium nitrate.
As disclosed in the referenced Patent Application, separate streams of the ammonia are fed to the nitric acid and ammonium nitrate producing stages. Also, in one embodiment of the disclosed process, steam that is generated in the course of concentrating an ammonium nitrate solution in the ammonium nitrate producing stage is transferred to the nitric acid producing stage to form at least a portion of the steam component of the oxidiser feed or to form a portion of a water or steam component of a starting feed from which the oxidiser feed is derived. As further disclosed in one embodiment, a small excess of ammonia may be supplied to the ammonium nitrate producing stage (for the purposes of minimising evaporator corrosion and suppression of the partial pressure of nitric acid in the vapour space of the evaporator) and, as a consequence, a small amount of ammonia (substantially less than 10% of the ammonia component of the oxidiser feed) might be fed to the nitric acid producing stage with the steam.
The present Inventors have now determined that, by feeding a substantial excess (i.e., at least 10%) of ammonia to the ammonium nitrate producing stage, the size of the ammonium nitrate reactor may be reduced, as may be the mixing precision requirement for complete reaction of the nitric acid. Also, it has been determined that the substantial excess of ammonia may usefully be fed from the ammonium nitrate producing stage to the nitric acid producing stage in a steam feed that comprises substantially the whole of that required by the nitric acid producing stage.
As also disclosed in the referenced Patent Application, the oxidising gas constituent of the oxidiser feed comprises a gas containing more than about 80% oxygen. However, the present Inventors have now determined that the oxidising gas may comprise air or another oxidising gas mixture that is less rich than 80% oxygen; accepting that the reaction-absorption volume will be substantially larger, but this being compensated by the potential for substantially reduced cost of employing a less oxygen-rich oxidising gas.